The present invention relates to an improved rotary machine for gravure printing.
Conventionally, rotogravure machines comprise a number of assemblies, each of which printing in one given color. Each such assembly comprises a print cylinder, bearing the image to be reproduced, which rotates with its bottom part immersed in a bath of ink in such a way that the ink is picked up and carried to the point of transfer, surplus ink being removed from the cylinder by a blade (the doctor); also forming part of the assembly is an impression cylinder, mounted usually above the print cylinder, by which a web of material running between the two cylinders is urged against the inked surface of the print cylinder.
In operation, the web is fed between the print and impression cylinders of each successive assembly in this manner, receiving one component color part of the composite image at each assembly as it passes through the machine.
With each printing run completed, preparation for another (with a different image) clearly involves changing over all the print cylinders.
Such a procedure is notably time-consuming, as the print cylinder has to be lifted from its bearings and the ink bath from its support, and replaced by the cylinder and bath needed for the next run, whereupon the new print cylinder must be correctly positioned, as also must be the doctor blade which removes surplus ink. Needless to say, the change procedure must be effected for each single station. Furthermore, the procedure outlined is rendered difficult by the fact that the print cylinder and ink bath are notably cumbersome and heavy.
With changeover in progress, the machine obviously must remain at a standstill, of duration dependent upon the number of individual cylinder assemblies; in effect, the interruption generally will be a matter of hours, and given the high purchase price of rotogravure equipment, every stoppage represents an increase in overheads which, in practice, denies cost-effective operation in the case of small jobs; at all events, down time will constitute a part of the costs in any contract undertaken, and persons skilled in the art know full well that where rotary printing equipment is involved, such costs run into hundreds of dollars per hour.
For some time now, the operation of changing over print cylinders and ink baths has been speeded up by the use of trolleys. Each cylinder and ink bath unit is carried by a relative trolley that can be positioned in the relative print station, thus facilitating set-up. The standard practice is to utilize two trolleys per station, such that while one trolley remains with the machine, in readiness for removal of the print cylinder and ink bath on completion of the run, the spare trolley can be equipped with a new cylinder and ink supply with which to replace the trolley removed.
With this arrangement, on completion of the run, the one cylinder and bath unit can be distanced from the machine using the first trolley, and the replacement unit moved into position in the machine using the second trolley; the replacement trolley having been thus brought into the machine, it remains to raise the cylinder and bath into the correct position, together with all the ancillary components.
Even with this method, the time needed to effect a changeover between jobs will never be less than two or three hours, especially where the rotary machine incorporates a significant number of stations. Accordingly, the object of the invention is to overcome the drawbacks described above by providing a rotogravure machine in which the time required to replace print cylinders is markedly reduced.